Paper articles exhibiting long term storageability and method for making same

ABSTRACT

A method for increasing the long term storageability of a cellulosic paper or paperboard product. The method includes providing a paper or paperboard product made from cellulosic fibers having a basis weight ranging from about 80 to about 300 pounds per 3000 square feet. A holdout material is applied to at least one surface of the paper or paperboard product. The web is then coated with an ink receptive material selected from the group consisting of an aqueous acrylic polymer coating material, an aqueous biocidal agent and a combination of aqueous acrylic polymer coating material and aqueous biocidal agent and dried to provide a paper or paperboard product having enhanced long term storageability. Webs made according to the invention are suitable for making file folders which exhibit improve long term storageability by resisting damage from moisture and/or biological activity.

[0001] This application claims the benefit of provisional applicationSerial No. 60/283,055, filed Apr. 11, 2001, of provisional applicationSerial No. 60/283,677, filed Apr. 12, 2001, and of provisionalapplication Serial No. 60/283,066, filed Apr. 11, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to the papermaking art and, in particular,to the manufacture of paper products having basis weights above about 80pounds per 3000 square feet up to and including about 300 pounds per3000 square feet, such as file folders, non-corrugated containers, andthe like, which exhibit improved properties for office environments andlong term storage.

BACKGROUND OF THE INVENTION

[0003] Heavy weight cellulosic paper and paperboard products such asfile folders and paperboard file containers are often subject to liquidor moisture damage during routine handling and long term storage. Inaddition, such products, if stored in a humid environment, tend tosupport biological growth which results in undesirable odors beingproduced. Furthermore, such products may be damaged or soiled by aqueousliquids thereby discoloring the paper or paperboard products. Ifmoisture or aqueous liquid are absorbed by the paper or paperboardmaterials, the materials may become soggy, warped and/or weakenedthereby reducing their usefulness and potentially allowing the liquidsto contact and damage documents which may be stored in containers madewith the paper or paperboard materials.

[0004] Accordingly, there exists a need for improved cellulose-basedproducts, and in particular relatively heavy weight paper and paperboardproducts, which exhibit improved resistance to moisture, water, and/ormicrobial growth.

SUMMARY OF THE INVENTION

[0005] With regard to the above and other objects and advantages, theinvention provides a method for increasing the long term storageabilityof a cellulosic paper or paperboard product. The method includesproviding a paper or paperboard product made from cellulosic fibershaving a basis weight ranging from about 80 to about 300 pounds per 3000square feet. A holdout material is applied to at least one surface ofthe paper or paperboard product to provide a sized web of paper orpaperboard. The sized web is then coated with an ink receptive materialselected from the group consisting of an aqueous acrylic polymer coatingmaterial, an aqueous biocidal agent and a combination of aqueous acrylicpolymer coating material and aqueous biocidal agent to provide an inkreceptive layer. Then the web is dried at a first temperature to providea coated web. In order to reduce web cur, an uncoated side of the web iswetted with an aqueous fluid and dried at a second temperature toprovide a paper or paperboard product having enhanced long termstorageability.

[0006] In another embodiment the invention provides a method forreducing microbial growth on stored paper or paperboard products. Themethod includes providing a paper or paperboard product made fromcellulosic fibers having a basis weight ranging from about 80 to about300 pounds per 3000 square feet. At least one surface of the paper orpaperboard product is sized with from about 0.5 to about 1.5 percent byweight starch sizing agent to provide a sized web of paper orpaperboard. The sized web is coated with an aqueous biocidal agent andthe web is dried to provide a paper or paperboard product having reducedtendency for microbial growth.

[0007] Another embodiment of the invention provides a paper orpaperboard composite having enhanced long term storageability. The paperor paperboard composite includes a base layer formed from a cellulosicfiber substrate, the base layer having a first surface, second surfaceand a basis weight ranging from about 80 to about 300 pounds per 3000square feet. A holdout layer is applied adjacent the first surface ofthe base layer. An ink receptive coating material is applied adjacentthe holdout layer to provide an ink receptive layer. The ink receptivecoating material is selected from the group consisting of an aqueousacrylic polymer coating material, an aqueous biocidal agent and acombination of aqueous acrylic polymer coating material and aqueousbiocidal agent.

[0008] An advantage of the invention is that relatively heavy weightpaper and paperboard products may be stored for a long term withoutsignificant deterioration or production of odor causing organisms. Theproducts of the invention also exhibit improved long term durability andresist damage and staining caused by water and other aqueous fluids.Another advantage of the invention is that paper and paperboard websmade according to the invention exhibit less tendency to slide relativeto one another as compared thermoplastic coated webs which are difficultto stack on one another because of their slick surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further advantages of the invention will become apparent byreference to the detailed description of preferred embodiments whenconsidered in conjunction with the drawings, which are not to scale,wherein like reference characters designate like or similar elementsthroughout the several drawings as follows:

[0010] FIGS. 1-3 are cross-sectional views not to scale of paper orpaperboard products according to the invention; and

[0011]FIG. 4 is a schematic flow diagram, not to scale, of a process formaking paper and paperboard products according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0012] With reference now to FIGS. 1-4, the invention provides a web 10having a holdout layer 12 and a print receptive layer 14, 18, or 20. Theprint receptive layer 14, 18, or 20 will be described in more detailbelow. Layer 16 is preferably a printed image layer which is applieddirectly to or adjacent to the print receptive layer 14, 18, or 20preferably by a printing process selected from a flexographic printer, alithographic printer, a rotogravure printer, and the like. Accordingly,the print receptive layer 14, 18, or 20 is preferably a lipophilic orhydrophobic print receptive layer. In an alternative, a printed imagemay be applied directly to the holdout layer 12 and the printed imagethen coated with the print receptive layer 14, 18, or 20. Thus the printreceptive layer 14, 18, or 20 of the alternative embodiment provides anadditional surface for accepting a printed image to complement the imageprinted on the holdout layer 12.

[0013] The web 10 is preferably a paper or paperboard web made ofcellulose fibers by a conventional papermaking process having a basisweight preferably ranging from about 80 to about 300 pounds per 3000square feet or more. Hence, the paper or paperboard is relativelyinflexible as compared to paper having a lower basis weight. Aparticularly preferred web 10 is a paperboard web used for making filefolders, manila folders, flap folders such as Bristol base paper, andother substantially inflexible paperboard webs for use in officeenvironments, including, but not limited to paperboard containers forsuch folders, and the like.

[0014] The web 10 is preferably coated rather than impregnated with theprint receptive layer 14, 18, or 20. Accordingly, after the web isformed, calendered and dried, a holdout layer 12 is preferably appliedto at least one surface of the web 10. If both surfaces of the web arecoated with the print receptive layer 14, 18, or 20, then the holdoutlayer 12 is preferably applied to both surfaces of the web 10. Thepreferred holdout layer 12 is provided by a sizing agent such as astarch sizing agent. When a starch sizing agent is used as the holdoutlayer 12, the sizing agent is preferably applied to a surface of the web10 using about 0.5 to about 1.5 weight percent starch size from a waterbox. The holdout layer 12 and method for applying the holdout layer 12to the web are not critical to the invention provided a holdout layer 12is provided which inhibits significant penetration or absorption of theprint receptive layer 14, 18, or 20 into the web 10.

[0015] With reference to FIG. 1, a preferred print receptive layer 14includes a layer made from an aqueous acrylic coating material includingan agent for reducing biological activity on the web 10. The acryliccoating material for providing layer 14 is preferably an acrylic polymeremulsion or dispersion in an aqueous carrier liquid. The acrylic polymeror emulsion preferably contains from about 35 to about 40 weight percentacrylic polymer solids and is preferably a film forming material whichis effective to increase the resistance of the web 10 to wetting withaqueous fluids. A particularly preferred acrylic polymer emulsionmaterial for providing layer 14 is available from Michelman, Inc. ofCincinnati, Ohio under the trade name MICRYL 474. The MICRYL 474 coatingmaterial has been used in the prior art as a paper coating for flexiblecement bags. The lightweight coated paper used for cement bags waslaminated to a plastic film for making the bag.

[0016] Whether or not layer 14 includes the biocidal agent, the acrylicpolymer coating material may also include other additives to improve theink receptability of the ink receptive layer 14. Such other additivesinclude, but are not limited to, silica, clay, polyvinyl alcohol orcross-linked acrylics. Layer 14 may be applied to the holdout layer 12by a wide variety of coating methods including, but not limited to, useof a flexographic coater, a rod coater, a rotogravure coater, an offsetcoater, a knife over roll coater, a lithographic coater, a dip coater,and a spray coater. The coating weight applied to the holdout layer 12is preferably in the range of from about 1.5 to about 3.0 pounds per3000 square feet to provide ink receptive layer 14.

[0017] An important property of the webs made according to the inventionis their water shedability or resistance to wetting by aqueous fluids.The resistance of the web to wetting by aqueous fluids is determined bythe Cobb Sizing Test, according to ASTM D-3285 (TAPPI T-441).Conventional, sized webs used for file folders have a five minute waterabsorption in the range of from about 50 to 70 grams per square meter ofpaper tested. The web 10 containing holdout layer 12 and print receptivelayer 14 preferably has a five minute water absorption in the range offrom about 30 to about 40 grams per square meter.

[0018] A tester for performing the Cobb sizing test consists of a hollowmetal cylinder or ring (100, 25 or 10 cm² inside area). A metal baseplate with a clamping device is used to hold the ring against the sampleof paper to be tested and a neoprene mat. Neoprene gaskets may be usedto seal the cylinder against the web when the test sample is uneven. Animportant component of the test apparatus is a solid stainless steelroller having a smooth face about 20 cm wide and weighing about 10 kg.Also used for the test are a 100 mL graduated cylinder, a balance withsensitivity of 0.01 grams or better, blotting paper, and a timer orstopwatch.

[0019] A sample of paperboard material to be tested is cut approximately12.5×12.5 cm square from the coated web. The sample is weighed andplaced on the neoprene mat. The cylinder is clamped upon the sample bylocking a crossbar in place and tightening two knobs. If sample materialis textured, a gasket is placed between the sample and cylinder,carefully aligning the inner edges of each. The test liquid, in thiscase preferably water is poured into the test cylinder. The amount oftest liquid is preferably 100 mL for 100 square centimeter cylinder.Proportionately less liquid is used for smaller cylinders. After pouringthe liquid, the timer is started to provide a five minute test. Longerand shorter test periods may be provided. At fifteen seconds before theexpiration of the predetermined test period, the liquid is quicklypoured from the cylinder, using care in not dropping any liquid on theuntreated (outside) portion of the test specimen. The cylinder isremoved from the sample and the sample is placed with wetted side up ona sheet of blotting paper.

[0020] At exactly the end of the predetermined test period, a secondsheet of blotting paper is placed on top of the sample to remove thesurplus liquid by moving the hand roller once forward and once backwardover the sample and blotting paper. Care should be taken not to exertdownward force on the roller. The specimen is then folded after removingit from between the blotter sheets and re-weighed to the nearest 0.01gram. The initial weight of the web is subtracted from the final weightof the sample and the gain in weight in grams is multiplied by 100 for a100 cm² cylinder to obtain the weight of liquid absorbed in grams persquare meter.

[0021] The resistance of the coated web to staining is determined bypouring a small amount of aqueous liquid such as coffee, soda, juiceonto the coated web. The aqueous fluid is then wiped off after 30seconds and the web is visually examined for evidence of staining orwarping. Webs produced according to the invention exhibited lessstaining with dark fluids and less warping than conventional webs.

[0022] The agent for reducing biological activity included in layer 14is preferably a haloalkynyl carbamate. A particularly preferredhaloalkynyl alkyl carbamate is a halopropynyl carbamate, most preferably3-iodo2-propynyl butyl carbamate available as a latex dispersion whereinthe active ingredient is present in the dispersion in an amount rangingfrom about 15 to about 30 percent by weight of the dispersion.Particularly preferred biocidal agents include aqueous dispersionsavailable from Buckman Laboratories of Memphis, Tenn. under the tradenames BUSAN 1420, BUSAN 1440, and BUSAN 1192D. Another preferredbiocidal agent is available from Troy Technology Corporation, Inc. ofWilmington, Del. under the trade names POLYPHASE 641 and POLYPHASE P100.Still another preferred biocidal agent is available from ProgressiveCoatings of Shreveport, La. under the trade name VJ2180N.

[0023] The biocidal agent may be applied to both surface of the web withor without the acrylic polymer coating material. In the embodimentrepresented by FIG. 1, the biocidal agent is mixed with the acrylicpolymer coating material in an amount preferably ranging is from about0.25 to about 4 weight percent of the total acrylic polymer coatingmaterial applied as layer 14.

[0024] After coating the web 10 and layer 12 with the acrylic polymercoating material, the web is dried to provide ink receptive layer 14 forreceiving print 16. The web is preferably dried in an oven or usingdrying rolls at a temperature ranging from about 110° to about 200° C.to provide a web temperature not to exceed about 85° C. The entirecoating and drying process is preferably conducted on a moving webrunning at about 300 to about 800 feet per minute or more.

[0025] In order to reduce web curl when only one side of the web 10 iscoated with the holdout layer 12 and ink receptive layer 14, it isparticularly preferred to wet the uncoated side of the web with anaqueous fluid such as water. In this case a minimal amount of water isused to wet the uncoated side of the web. A minimal amount of water maybe applied to the uncoated side of the web using, for example, a zerorod.

[0026] In the embodiment illustrated in FIG. 2, the web 10 includesholdout layer 12 and ink receptive layer 18. The ink receptive layer 18is preferably provided by coating the holdout layer 12 with the abovedescribed film forming acrylic polymer material without the biocidalagent incorporated in the acrylic polymer material. Accordingly, theproduct illustrated in FIG. 2 is also receptive to a print layer 16 andexhibits a similar resistance to wetting as the web described withreference to FIG. 1 above.

[0027]FIG. 3 illustrates an embodiment of the invention wherein the inkreceptive layer 20 is provided by coating the holdout layer 12 with anaqueous dispersion containing the biocidal agent described above. Inthis case, the holdout layer 12 is preferably coated with the biocidalagent provided as a latex coating material using a flexographic coater,a blade-over-roll coater, a rotogravure coater, or an applicator rollcoater. The preferred coater is a flexographic coater having an aniloxcylinder containing at least about 250 cells per linear inch, each cellhaving a volume of about 7.0 billion cubic microns per square inch(bcm). The line speed for the coater is preferably about 200 to 300 feetper minute or higher. After coating the web with the ink receptive layer20, the web is dried as above in an oven or using drying rolls at atemperature ranging from about 110° to about 200° C. to provide a webtemperature not to exceed about 8520 C. When the web is coated with onlythe biological activity reducing agent, it is particularly preferred tocoat both surface of the web 10. Accordingly, the holdout layer 12 ispreferably applied to both surface of the web 10.

[0028] A process for making webs according to the invention isillustrated in FIG. 4. A web for use according to the invention is madeby a conventional papermaking process.

[0029] Accordingly, the web may be formed on a papermaking machine 30from a furnish 32 provided to a headbox 34 to yield formed web 36. Theformed web 36 is calendered by calender rolls 38 to provide calenderedweb 40. The calendered web 40 is then dried in web dryer 42 to provide adried web 44. The dried web 44 is then sized by sizing rolls 46 toprovide a web 48 containing holdout layer 12. Next, the web 48 is coatedwith ink receptive layer 14, 18, or 20 by coater 50 to provide coatedweb 52. The coating material 54 is preferably applied to the web 48using coater 50. After coating the web, the coated web 52 is dried indryer 56 to provide web 58 having an ink receptive layer as describedabove.

[0030] As set forth above, if only one side of the web is coated withthe ink receptive layer 14, 18, or 20 and holdout layer 12, then it ispreferred to rewet the uncoated side of the web with an aqueous fluidand redry the web to reduce web curl.

[0031] In the following example, uncoated paper was coated with MICRYL474 coating from Michelman, Inc. using a number three rod, and the webwas dried by forced air having an air temperature of about 176° C. toprovide a coated web. Next, the uncoated side of the web was wet withwater using a zero rod. The web as then dried at about 120° to reduceweb curl. The coating an wetting steps were conducted on line at about400 feet per minute. The watershedability of the coated web wasdetermined according to the five minute Cobb sizing test describedabove. The results are given in the following table. TABLE Uncoatedpaper basis Coating weight of MICRYL 5-minute Cobb weight in pounds per474 coating in pounds per value in grams Sample No. 3000 square feet3000 square feet per square meter 1 124 2.5 32 2 143 1.5 35

[0032] As shown by the foregoing examples, paper coated with as littleas 1.5 pounds per 3000 square feet of the MICRYL 474 coating materialprovided reduced water absorption as compared to conventional uncoatedwebs which have a water absorption in the range of from about 55 toabout 60 grams per square meter as determined by the five minute Cobbsizing test.

[0033] Having now described various aspects of the invention andpreferred embodiments thereof, it will be recognized by those ofordinary skill that numerous modifications, variations and substitutionsmay exist within the spirit and scope of the appended claims.

What is claimed is:
 1. A method for increasing the long termstorageability of a cellulosic paper or paperboard product, comprisingthe steps of providing a paper or paperboard product made fromcellulosic fibers having a basis weight ranging from about 80 to about300 pounds per 3000 square feet, applying a holdout material to at leastone surface of the paper or paperboard product to provide a sized web ofpaper or paperboard, coating the sized web with an ink receptivematerial selected from the group consisting of an aqueous acrylicpolymer coating material, an aqueous biocidal agent and a combination ofaqueous acrylic polymer coating material and aqueous biocidal agent toprovide an ink receptive layer, drying the web at a first temperature toprovide a coated web, wetting an uncoated side of the web with anaqueous fluid to reduce web curl, and drying the web at a secondtemperature to provide a paper or paperboard product having enhancedlong term storageability.
 2. The method of claim 1 wherein the inkreceptive layer comprises an aqueous acrylic polymer coating materialhaving a solids content ranging from about 30 to about 45 percent byweight.
 3. The method of claim 2 wherein the aqueous acrylic polymercoating material comprises a film forming aqueous acrylic polymercoating material.
 4. The method of claim 1 wherein the web is coatedwith an aqueous biocidal agent comprises a haloalkynyl carbamate latexemulsion.
 5. The method of claim 4 wherein the aqueous biocidal agentcomprises a latex emulsion containing from about 20 to about 30 percentby weight active biocidal ingredient.
 6. The method of claim 1 whereinthe ink receptive material is applied to the web in an amount rangingfrom about 1.5 to about 3.0 pounds per 3000 square feet.
 7. The methodof claim 1 wherein the web is dried at a first temperature ranging fromabout 150° to about 200° C. to provide a web temperature not exceedingabout 85° C.
 8. The method of claim 1 wherein the second temperature islower than the first temperature.
 9. The method of claim 1 wherein theink receptive material is applied to the web using a coating processselected from the group consisting of a flexographic coater, a rodcoater, a rotogravure coater, an offset gravure coater, a knife overroll coater, a lithographic coater, a dip coater, and a spray coater.10. The method of claim 1 wherein the ink receptive material is appliedto the web using a size press.
 11. A paper or paperboard product made bythe method of claim
 1. 12. A paper or paperboard composite havingenhanced long term storageability comprising: a base layer formed from acellulosic fiber substrate, the base layer having a first surface,second surface and a basis weight ranging from about 80 to about 300pounds per 3000 square feet, a holdout layer adjacent the first surfaceof the base layer, and an ink receptive layer adjacent the holdoutlayer, the ink receptive layer being selected from the group consistingof an aqueous acrylic polymer coating material, an aqueous fungicide anda combination of aqueous acrylic polymer coating material and aqueousfungicide.
 13. The composite of claim 12 further comprising a printedimage layer applied to the ink receptive layer.
 14. The composite ofclaim 12 further comprising a printed image layer disposed between theholdout layer and the ink receptive layer.
 15. The composite of claim 12wherein the ink receptive layer comprises an aqueous, film formingacrylic polymer layer provided by a coating ink receptive coatingmaterial having a solids content ranging from about 30 to about 45percent by weight.
 16. The composite of claim 12 wherein the inkreceptive layer comprises an aqueous biocidal agent.
 17. The compositeof claim 16 wherein the aqueous biocidal agent comprises3-iodo-2-propynyl butyl carbamate.
 18. The composite of claim 12 whereinthe composite comprises a file folder.
 19. A method for reducingmicrobial growth on stored paper or paperboard products comprisingproviding a paper or paperboard product made from cellulosic fibershaving a basis weight ranging from about 80 to about 300 pounds per 3000square feet, applying from about 0.5 to about 1.5 percent by weightstarch sizing agent to at least one surface of the paper or paperboardproduct to provide a sized web of paper or paperboard, coating the sizedweb with an aqueous biocidal agent and drying the web to provide a paperor paperboard product having reduced tendency for microbial growth. 20.The method of claim 19 wherein the aqueous biocidal agent comprises alatex coating material containing from about 15 to about 30 percent byweight active biocidal agent.
 21. The method of claim 19 wherein bothsurfaces of the paper or paperboard product are coated with the starchsizing agent and aqueous biocidal agent.
 22. A method for improving thewater-shedability of paper or paperboard products comprising providing apaper or paperboard web made from cellulosic fibers having a basisweight ranging from about 80 to about 300 pounds per 3000 square feet,applying from about 0.5 to about 1.5 percent by weight starch sizingagent to at least one surface of the paper or paperboard web to providea sized web of paper or paperboard, coating the sized web with an inkreceptive coating material to provide an ink receptive layer, and dryingthe coated and sized web at a first temperature to provide a paper orpaperboard product having improved water-shedability, whereby theproduct exhibits a liquid resistance ranging from about 30 to about 40grams per square meter water absorbence as measured by a Cobb Sizingtest.
 23. The method of claim 22 wherein the ink receptive layercomprises an aqueous acrylic polymer coating applied in an amountranging from about 1.5 to about 3.0 pounds per 3000 square feet of paperor paperboard web.
 24. The method of claim 22 further comprising wettingan uncoated side of the web with an aqueous fluid to reduce web curl,and drying the web at a second temperature.
 25. The method of claim 22wherein both surfaces of the web are coated with the sizing agent andink receptive coating material.
 26. A file folder formed according tothe method of claim 22.